A density functional theory investigation of CrSin (n=1–6) clusters

Clusters of the form CrSi_n (n=1–6) were investigated computationally using a density functional approach. In particular, geometry optimizations were carried out under the constraint of well-defined point group symmetries at the B3LYP level employing a pseudopotential method in conjunction with double zeta basis sets. In this article, the resulting total energies, Mulliken atomic net populations, overlap populations, fragmentation energies and geometries of CrSi_n (n=1–6) are presented and discussed, together with natural populations and natural electron configurations. In addition, we comment on the charge transfer within the clusters. From this analysis, the 3d orbital of the Cr atom in CrSi_n (n=1–6) cluster absorbs electrons. From this tendency, conclusions are drawn with respect to the electronic populations and the chemical bond between Si and Cr as well as Si and Si.     

A density functional theory study of the Cu+·(CO)n (n = 1–3) complexes

Density functional theory calculations, with an effective core potential for the copper ion, and large polarized basis set functions have been used to construct the potential energy surface of the Cu⁺·(CO)_n (n = 1–3) complexes. A linear configuration is obtained for the global minimum of the Cu⁺·CO and Cu⁺·(CO)₂ complexes with a bond dissociation energy (BDE) of 35.9 and 40.0 kcal mol^-1, respectively. For the Cu⁺·(CO)₃ complex, a trigonal planar geometry is obtained for the global minimum with a BDE of 16.5 kcal mol^?1. C-coordinated copper ion complexes exhibit stronger binding energy than O-coordinated complexes as a result of C_lp → 4s σ-donation. The computed sequential BDEs of Cu⁺·(CO)_n (n = 1–4) complexes agree well with experimental findings, in which the electrostatic energy and σ-donation play an important role in the observed trend.     

Assessment of multicoefficient correlation methods, second-order Møller-Plesset perturbation theory, and density functional theory for H3O(+)(H2O)n (n = 1-5) and OH(-)(H2O)n (n = 1-4)

We have assessed the ability of 52 methods including 15 multicoefficient correlation methods (MCCMs), two complete basis set (CBS) methods, second-order M?ller-Plesset perturbation theory (MP2) with 5 basis sets, the popular B3LYP hybrid functional with 6 basis sets, and 24 combinations of local density functional and basis set to accurately reproduce reaction energies obtained at the Weizmann-1 level of theory for hydronium, hydroxide, and pure water clusters. The three best methods overall are BMC-CCSD, G3SX(MP3), and M06-L/aug-cc-pVTZ. If only microsolvated ion data is included, M06-L/aug-cc-pVTZ is the best method; it has errors only half as large as the other density functionals. The deviations between the three best performing methods are larger for the larger hydronium- and hydroxide-containing clusters, despite a decrease in the average reaction energy, making it impossible to determine which of the three methods is overall the best, so they might be ranked in order of increasing cost, with BMC-CCSD least expensive, followed by M06-L/aug-cc-pVTZ. However, the cost for M06-L will increase more slowly as cluster size increases. This study shows that the M06-L functional is very promising for condensed-phase simulations of the transport of hydronium and hydroxide ions in aqueous solution.     

Electronic structure and stability of anionic AuGen (n = 1–20) clusters and assemblies: a density functional modeling

Structural Chemistry - In the present study electronic structure and stabilities of cationic gold-doped germanium clusters, AuGen (n?=?1 to 20), and their assemblies have been...     

Density functional theory study on (F2AlN3) n (n = 1–4) clusters

Possible geometrical structures and relative stabilities of (F₂AlN₃) _n (n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F₂AlN₃) _n (n = 2–4) possess cyclic structure containing Al–N_α–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F₂AlN₃) _n (n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm⁻¹, and the vibrational modes are N₃ asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters (2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K.     

Structure–antioxidant activity relationships of dendrocandin analogues determined using density functional theory

Structural Chemistry - Quantum-chemical calculations based on the density functional theory (DFT) at the B3LYP/6–311?+?+?G(2d,2p)//B3LYP/6–31G(d,p) level were employed...     

Density functional theory study of the structures,electronic states and stabilities of Al n Pt (n = 1–15) clusters

The binding energy, dissociation energy, ionization potentials, electron affinities, gap and stability of small Al _n Pt (n = 1–15) clusters, in comparison with pure aluminum clusters have been systematically investigated by means of density functional calculations at the B3LYP level. The growth patten for Al _n Pt clusters is that the Pt atom substituted the surface atom of the Al _{n + 1} clusters for n < 13. Starting from n = 13, the Pt atom completely falls into the center of the Al-frame. The Pt atom substituted the center atom of the Al _{n + 1} clusters to form the Pt-encapsulated Aln geometries for n > 13. We also find that the impurity Pt atom causes local structural distortion due to different atomic radii and different bonding characteristics. The clusters with total atom numbers of 2, 7, and 11 exhibit high stability.     

Theoretical study of the stability and electronic structure of Al(BH4)n=1→4 and Al(BF4)n=1→4 and their hyperhalogen behavior

Using density functional theory (DFT), we have systematically calculated the equilibrium geometries, electronic structure, and electron detachment energies of Al(BH(4))(n=1→4) and Al(BF(4))(n=1→4) at the B3LYP/6-311+G(2d,p) level of theory. The electron affinities of Al(BH(4))(n) not only exhibit odd-even alternation, just as seen in (BH(4))(n), but also, for n = 3 and 4, show a remarkable behavior: whereas the electron affinities of BH(3) and BH(4) are, respectively, 0.06 and 3.17 eV, those of Al(BH(4))(3) and Al(BH(4))(4) are 0.71 and 5.56 eV. Results where H is replaced by F are also very different. The electron affinities of BF(3) and BF(4) are, respectively, -0.44 and +6.86 eV, and those of Al(BF(4))(3) and Al(BF(4))(4) are 1.82 and 8.86 eV. The results demonstrate not only marked difference when H is replaced by F but also substantially enhanced electron affinities by almost 2 eV when BH(4) and BF(4) units are allowed decorate a metal atom, confirming the recently observed hyperhalogen behavior of superhalogen building blocks.     

Structures,stabilities, and electronic properties of Al n Au (n = 1–15) clusters: A density functional study

We present density functional calculations of Al _n Au clusters for n = 1–15. The growth pattern for Al _n Au (n = 1–7, 12, 14, 15) clusters is the Au atom occupying a peripheral position of Al _n clusters, and the growth pattern for Al _n Au (n = 8, 10 and 13) clusters is Au-substituted Al _n+1 clusters. It is found that the Au atom replaces the surface atom of an Al _n+1 cluster and occupies a peripheral position. In addition, the ground state structures of Al _n Au clusters are more stable than pure Aln clusters. It is found that the Al₁₃Au cluster exhibits high stability.     

The density functional theory study CO oxidation catalyzed by subnanometer AlAg n (n = 1–3) clusters

The efficiency of AlAg _n (n = 1–3) alloy clusters toward CO oxidation is demonstrated from first-principles theory. It is found that these subnanometer species transform into reaction complexes which catalyze CO oxidation through the Langmuir–Hinshelwood path. It is shown that mixing two different metals (Al and Ag) can have beneficial effects on the catalytic activity and the alloyed AlAg₃ cluster is proposed as the best effective nanocatalysts.     

A computational study on CunN0,±1 (n=1–4) clusters by density functional methods

Clusters of the type Cu_nN^0,±1 (n=1–4) are investigated computationally using density functional theory methods. Equilibrium geometries are optimized under the constraint of well-defined point-group symmetries at the B3LYP level employing a pseudo-potential method in conjunction with double-zeta basis sets. In this article, different molecular properties such as total energies, electron affinities, ionization potentials, fragmentation energies and equilibrium geometries of the Cu_nN^0,±1 (n=1–4) clusters are systematically calculated and discussed. In particular, the photoelectron spectra of the anionic Cu_nN⁻¹ (n=2–4) clusters are calculated showing a good agreement with the available experimental results. In addition, Mulliken and natural orbital population analyses, and natural orbital configurations are calculated in order to elucidate the charge distributions in the clusters.     

Quantum chemical calculations and the structure of Ni n (C2H2) complexes (n = 1–4)

Complexes of nickel atoms and small clusters with acetylene molecules are studied within the density functional theory. A trend toward the predominant formation of structures with bridge hydrogen atoms is observed in reactions between Ni _n and acetylene with rising n.     

Heats of formation for Fe(CO)n(n=1–4)

The dissociation energies of Fe(CO)_n (n=2–4) are computed using correlation consistent basis sets and the CCSD(T) approach. The dissociation energies are extrapolated to the CBS limit and are corrected for core–valence (CV), scalar relativistic, spin–orbit, zero-point, and thermal effects. Our iron carbonyl bond strengths agree with experiment within the respective error bars. We use our dissociations energies at 298 K to obtain the heats of formation of Fe(CO)_n (n=1–4).     

Structure and stability for (AlN)_n~+ and (AlN)_n~- (n=1-15) clusters

Using density functional theory (DFT) method with 6-31G* basis set, we have carried out the optimizing calculation of geometry, vibrational frequency and thermodynamical stability for(AIN)n+ and (AIN)n- (n =1-15) clusters. Moreover, their ionic potential (IP) and electron affinity(EA) were discussed. The results show that the electrical charge condition of the cluster has a relatively great impact on the structure of the cluster and with the increase of n, this kind of impactis reduced gradually. There are no AI-AI and N-N bonds in the stable structure of (AIN)n+ or (AIN)n-, and the AI-N bond is the sole bond type. The magic number regularity of (AIN)n+, and (AIN)n- is consistent with that for (AIN)n, indicating that the structure with even n such as 2, 4,6, … is more stable. In addition, (AIN)10 has the maximal ionization power (9.14 eV) and the minimal electron affinity energy (0.19 eV), which manifests that (AIN)10 is more stable than other clusters.     

Surface-enhanced Raman scattering of M2–pyrazine–M2 (M = Cu,Ag, Au): Analysis by natural perturbation orbitals and density functional theory functional dependence

Here, we propose a new method to analyze various electronic properties of molecules based on natural perturbation orbitals (NPOs). We applied the proposed method to chemical enhancement of the surface-enhanced Raman scattering (SERS) intensity of M₂–pyrazine–M₂ (M = Cu, Ag, Au) complexes. The SERS intensity can be effectively decomposed into the contributions of four NPO pairs (1σ–1σ*, 2σ–2σ*, 1π–1π*, and 2π–2π*), so NPO analysis makes the SERS intensity much easier to understand than by conventional canonical molecular orbitals. Moreover, we analyzed the dependence of the density functional theory functional on the SERS intensity. For the Ag₂–pyrazine–Ag₂ complex, the BP86 functional overestimates the Raman intensity by about 23 times compared with coupled-cluster singles and doubles level of theory, while the CAM-B3LYP functional gives moderately accurate values. This overestimation arises from the inaccuracy of the energy derivative along the normal vibrational mode.     

Structure, stability and electronic property of the gold-doped germanium clusters: AuGe n (n = 2–13)

The structure, stability and electronic property of the AuGe _n (n = 2–13) clusters with different spin configurations are systematically investigated with density-functional theory approach at UB3LYP/LanL2DZ level. In examining the lowest energy structures, it is found that the growth behaviors for the small-sized AuGe _n (n = 2–9) clusters and relatively large-sized AuGe _n (n = 10–13) clusters are different. As the number of Ge atom increases, the Au atom would gradually move from convex to surface and to interior sites. For the most stable structures of AuGe _n (n = 10–13) clusters, the Au atom would be completely surrounded by the Ge atoms to form Au-encapsulated Ge _n cages. Natural population analysis shows that the charges always transfer from the Au atom to the Ge _n framework except for the AuGe₂ cluster. This indicates that the Au atom acts as electron donor even the 5d orbitals of the Au atom are not significantly involved in chemical bonding. The analyses of the average atomic binding energies as well as the dissociation energies and the second-order differences of total energy show that the AuGe _n clusters with n = 5, 9 and 12 are more stable than their neighboring ones, in which the bicapped pentagonal prism AuGe₁₂ in D _2d symmetry is most stable. The highest occupied molecular orbital–lowest unoccupied molecular orbital gaps are explored to be in the region of semiconductors and the more stable clusters have slightly smaller gaps. It could be expected that the stable clusters might be considered as the novel building blocks in practical applications, e.g., the cluster-assembled semiconductors or optoelectronic material.     

Theoretical study on the structures and properties of (Br2AlN3) n (n = 1–4) clusters

To look for the single-source precursors, the structures and properties of (Br₂AlN₃) _n (n = 1–4) clusters are studied at the B3LYP/6-311+G* level. The optimized (Br₂AlN₃) _n (n = 2–4) clusters all possess cyclic structures containing Al-N_α-Al linkages. The relationships between the geometrical parameters and the oligomerization degree n are discussed. The gas-phase structures of the trimers prefer to exist in the boat-twisting conformation. As for the tetramer, the most stable isomers have the S ₄ symmetry structure. The IR spectra are obtained and assigned by the vibrational analysis. The thermodynamic properties are linearly related with the oligomerization degree n as well as with the temperature. Meanwhile, the thermodynamic analysis of the gas-phase reaction suggests that the oligomerization be exothermic and favorable under high temperature.     

Structure and stability of AuXe n Z (n = 1–3, Z = −1, 0, +1) clusters

We have explored the structures and stabilities of AuXe _n ^Z (n = 1–3, Z = ?1, 0, +1) cluster series at CCSD(T) theoretical level. The electron affinities and ionization potentials are correlated to the HOMO–LUMO gaps. The role of the interaction was investigated using the natural bond orbital analysis.     

Density functional investigations on the (H2O)n·CCH and (H2O)n·HCC complexes (n=1–3)

The electronic structures and energies of (H₂O)_n·CCH and (H₂O)_n·HCC complexes (n=1–3) between CCH and water have been theoretically investigated at the UB3LYP/6-311++G(2df,p)//UB3LYP/6-311G(d,p) level. The complexes with n=2–3 are cyclic structures with homodromic hydrogen-bond chain. The (H₂O)_n·CCH (n=1–3) complexes show increasing stabilities towards CCH- or H₂O-eliminations of 2.3, 5.8 and 7.6 kcal/mol and are energetically more stable than the corresponding (H₂O)_n·HCC complexes by 0.8, 2.7 and 3.4 kcal/mol, respectively, due to the charge-separation-enhanced hydrogen bonds within (H₂O)_n·CCH (n=2,3). Strong interactions between CCH and (H₂O)₂ and (H₂O)₃ clusters suggest special solvent effects of water on the chemical behavior of unsaturated radicals.